1. Field of the Invention
The present invention relates to a reference signal oscillator which outputs a reference signal.
2. Description of the Related Art
In a base station of a radio communication system, a reference frequency signal having quite a high frequency stability is required, and thus an expensive oscillator such as a rubidium oscillator or a cesium oscillator is used. On the other hand, as a countermeasure against a trouble of the oscillator, there is adopted a redundant constitution in which duplexed oscillators as above are provided. Though a long-term frequency stability of such type of an oscillator is superior, it takes a long time since power application until a frequency becomes stable and its frequency stability for a short term is poor, and thus a backup oscillator is on standby in a state of power-on and being oscillating.
However, when the rubidium oscillator or the cesium oscillator is used as the backup, there is a problem that a price of the system becomes quite high.
Patent Document 1 describes a technique to include both TCXO and OCXO in a frequency synthesizer and to switchingly use the above as a reference signal, and Patent Document 2 describes a technique to include a voltage control digital temperature compensated oscillator and an OCCO and to switchingly use the above as a reference signal, but indication of the present invention is not given therein.    [Patent Document 1] Japanese Patent Application Laid-open No. Hei 8-56120    [Patent Document 2] Japanese Patent Application Laid-open No. 2004-172686